Field of the Invention
The present invention relates to a laundry treatment apparatus.
Discussion of the Related Art
A conventional laundry treatment apparatus includes a cabinet defining an external appearance of the laundry treatment apparatus, a tub installed within the cabinet, a drum rotatably installed within the tub, the drum serving to wash laundry therein, and a motor, a rotating shaft of which penetrates the tub and is secured to the drum to rotate the drum.
The drum may fail to maintain dynamic equilibrium or dynamic balance according to a position of laundry stored therein, which may cause unintentional rotation of the drum.
Dynamic balance refers to a state in which centrifugal force or moment of centrifugal force becomes zero with respect to a rotation axis during rotation of a rotator. In the case of a rigid body, it maintains dynamic balance when mass distribution is constant about a rotation axis thereof.
Accordingly, with regard to the aforementioned laundry treatment apparatus, dynamic balance may be understood as a case in which mass distribution of laundry stored in the drum about a rotation axis of the drum falls within an acceptable range during rotation of the drum (i.e. a case in which the drum is rotated while undergoing vibration within an acceptable range).
On the other hand, breakage of dynamic balance (i.e. unbalance) with regard to the laundry treatment apparatus may be understood as a case in which mass distribution of laundry about a rotation axis of the drum is not constant during rotation of the drum. Such unbalance occurs when laundry is not uniformly distributed in the drum.
When the drum is rotated in an unbalanced state, vibration of the drum occurs, and in turn vibration of the drum is transferred to the tub or the cabinet, causing noise.
Some conventional laundry treatment apparatuses are equipped with balancers to eliminate unbalance of the drum. These balancers provided in some conventional laundry treatment apparatuses are ball balancers or fluid balancers in which a ball or liquid is received in a balancer housing that is mounted to the drum.
The drum in an unbalanced state has a feature in that revolutions per minute of the drum reach maximum when laundry, which induces unbalance of the drum, passes the lowermost point of a drum rotation trace, and reach minimum when the unbalance inducing laundry passes the uppermost point of the drum rotation trace.
Therefore, the ball balancers or fluid balancers equipped in the conventional laundry treatment apparatuses are devised to control unbalance as the ball or fluid moves to the lowermost point of the drum rotation trace when the unbalance inducing laundry moves to the uppermost point of the drum rotation trace.
The unbalance control described above may be available under steady state vibration in which vibration of the drum falls within a constant range. However, it is impossible to anticipate great effects in a transient vibration state before vibration of the drum reaches a steady state.
In addition, the conventional balancers have a difficulty in immediately eliminating occurred unbalance (i.e. in actively eliminating unbalance).